QUARTZ-CRYSTAL MICROBALANCE FOR THE DETECTION OF MICROGRAM QUANTITIES OF HUMAN SERUM-ALBUMIN - RELATIONSHIP BETWEEN THE FREQUENCY CHANGE AND THE MASS OF PROTEIN ADSORBED

We have developed a piezoelectric immunosensor for the detection of microalbumin. Human serum albumin (HSA) in the range 0.1-100 mug mL-1 could be detected using a flow cell; the immunosensor is sensitive enough to monitor levels of albuminuria. The immunosensor did not respond to bovine serum albumin, only to HSA, implying that the specificity for HSA was high. We investigated the relationship between the frequency change (DELTAF) and adsorption per unit area of piezoelectrically active quartz crystal (DELTAM). DELTAM was estimated with radioisotope-labeled anti-HSA or HSA. When anti-HSA was adsorbed onto the surface of the crystal or HSA was bound to anti-HSA supported by the crystal, values of \DELTAF/DELTAM\ were larger than the value predicted from theory (Sauerbrey's equation). Furthermore, \DELTAF/DELTAM\ for HSA was larger than that for anti-HSA.